The invention relates to a selector switch which may be configured as a distributed crossbar switch with redundancy or used to detect serial data at gigabit-per-second (Gb/s) rates from a selected one of a plurality of data lines.
With the advent of the dawn of the Information Highway and the explosion of telecommunications, the quantity and speed of data transmission continues to grow. In the telecommunications industry, as well as in the computer industry, there exists a need to transmit large quantities of data from point to point such as, for example, between memory and processors in a multi-processor computer. The large number of data bits coupled with the large number of connections create an interconnect bottleneck which requires large numbers of data drivers necessitating a large amount of electrical power. To overcome this interconnect congestion large numbers of parallel bit streams can be multiplexed to higher rate serial bit streams, thus reducing the number of electrical connections that need to be made. The need for low power multiplex and demultiplex circuits capable of combining data signals at high transmission rates, from 50 Mb/s to 1 Gb/s for example, has attracted a number of commercial integrated circuit vendors. Nevertheless, the computer and communications industry continues to search for lower power solutions.
A technique that has been employed with some success to reduce the number of interconnections in communications switching equipment is the employment of contactless, or non-contact, backplanes (the backplanes being sets of data lines). Non-contact backplanes permit point-to-multipoint and multipoint-to-point data transmission over a passive backplane without loss of signal integrity due to the multipoint connections. With this technique, distribution of multi-Gb/s serial data is achieved through a form of AC coupling of such small proportions that the data information is contained in the data transitions. It is not uncommon for the received data at the demultiplex circuit to be considerably attenuated by using this technique. Signal levels of only 70 mV peak to peak, or even less, are not uncommon. Reliable reception of the data requires special techniques including signal amplification, wide frequency bandwidth, matched input impedance and some form of hysteresis to discriminate against unwanted noise signals. Moreover, the resultant signal may need to be restored to Non-Return to Zero (NRZ) format from a Return to Zero (RZ) format. A receiver capable of such techniques is disclosed in U.S. Pat. No. 5,852,637 issued on Dec. 22, 1998 to Brown et al; U.S. patent application Ser. No. 09/054,440 filed Apr. 3, 1998 for xe2x80x9cA Multi-Gb/s Data Pulse Receiverxe2x80x9d; U.S. patent application Ser. No. 09/071,117 filed on May 4, 1998 for xe2x80x9cMethod and Apparatus for Performing Data Pulse Detectionxe2x80x9d; and U.S. patent application Ser. No. 09/238,893 filed on Jan. 28, 1999 for xe2x80x9cData Pulse Receiverxe2x80x9d, the contents of each of which are hereby incorporated herein by reference.
The application of a multi-Gb/s data pulse receiver (a xe2x80x9cMGDP Receiverxe2x80x9d) to enable the reception of RZ (return to zero) pulses from the AC couplers of the contactless backplane has permitted the performance of reliable point to multipoint distribution of high speed data buses in the Gb/s range. The AC coupling technique is based on directional coupling principles wherein data transfer occurs between proximate conductors. An example of one such coupling connector is described in U.S. Pat. No. 5,432,486 which issued Jul. 11, 1995 to Wong and assigned to Northern Telecom Limited. Typical bit error rate measurements per data line have been estimated to be as low as 10xe2x88x9221.
However, a problem with known non-contact backplane distribution systems is that they are limited to providing point to multipoint and multipoint to point applications and do not provide switching or redundancy.
We have recognised that it would be desirable to combine a non-contact backplane distribution system with a selector switch for selecting a data line from a plurality of data lines (hereinafter a xe2x80x9cbit line selector switchxe2x80x9d or xe2x80x9cswitchxe2x80x9d). The result would be a distributed crossbar switch with redundancy (i.e. no central switch fabric) that provides multicast and linear growth capabilities. However, current bit line selector switches are ill-suited for use in such a distributed cross-bar switch as they cause spurious reflections at the interface with the data lines. These reflections would lower the signal integrity and also limit the multicast ability of the cross-bar switch as the reflections induced by the bit line selector switch will corrupt the signals transmitted on the plurality of data lines affecting other receivers downstream.
The present invention relates to a bit line selector switch connected to a backplane to form a distributed crossbar switch. The cross-bar switch, which has no central switch fabric, provides redundancy and multicast and linear growth capability.
A selector switch is in non-contact communication, via a form of AC coupling, with at least one of the data lines forming the backplane. In an alternative embodiment, the selector switch is in non-contact communication with several of the data lines forming the backplane. The selector switch may also be combined with a converter for converting an RZ signal to the NRZ format prior to the transmission of the data pulse to a data sink such as, for example, a memory device, another processor, or the like (in which case the data sink does not effect this conversion).
The selector switch presents to an incoming signal, that is, a data pulse, an impedance that matches that of the input data line regardless of whether or not the data line input to the selector switch is to be selected. This impedance matching is accomplished by having two modes of operation of the selector switch. These two modes of operation may be enabled by connecting a resistor, which matches the impedance of the input data line, connected to two grounded base amplifiers, in parallel with each other, whose emitters are both connected to the other end of the resistor. If the input to the selector switch is a differential input, this resistor and parallel amplifier configuration is repeated for each side of the differential input.
In the first mode of operation, the OFF or xe2x80x9cnot selectedxe2x80x9d mode, a data line is not selected for reception and transmission of the data pulse to the data sink. In this mode of operation, the signal is transmitted first through the resistor and then into one of the grounded base amplifiers which will have its collector connected to a positive power supply. In this way, any signals received in this mode will be ignored by the system.
In the second mode of operation, the ON or xe2x80x9cselectedxe2x80x9d mode, a data line is selected for reception and transmission to, if incorporated, the RZ to NRZ converter, and then the data sink. In this mode an incoming signal is transmitted first through the resistor and then through the other grounded based amplifier to the converter, if incorporated, then to the data sink.
The selector switch""s mode may be dependent upon the reference bias voltages applied to the base of the amplifiers. In the first mode of operation the bias voltage applied to the amplifier connected to the positive supply is higher than that of the second bias voltage applied to the base of the second amplifier. In the second mode of operation the opposite is true.
According to one aspect of the invention there is provided a combined bit line selector switch and data pulse receiving system comprising: a plurality of data lines for the propagation of data pulses; and a bit line selector switch interconnecting the plurality of data lines and the receiver. The bit line selector switch comprises: switch inputs in non-contact communication with the plurality of data lines by a plurality of data line interconnects; and a switch output in communication with the receiver. For each of the switch inputs there is a selector circuit between each of the switch inputs and the switch output which have a first mode of operation wherein data pulses detected by the selector circuit are blocked and a second mode wherein the data pulses detected by the selector circuit are transmitted; and the at least one input selector circuit matching the impedance of the data line interconnect in either the first or the second modes.
Another aspect of the invention is a crossbar switch comprising: N data lines for propagation of data pulses; a receiver receiving the data pulses; a bit line selector system in non-contact communication with each of the N data lines so as to interconnect the receiver and the data coupling lines. The bit line selector system is operable to transmit the data pulses from a selected one of the N data lines to the receiver and to simultaneously block data pulses on the remaining Nxe2x88x921 data lines. The bit line selector system has N inputs corresponding to the N data coupling lines and an output in communication with the receiver. Moreover, the selector system matches the impedance of said N data coupling lines.
The selector system of this crossbar may be comprised of several stages, each stage being comprised of at least one selector switch in communication with another stage which is also comprised of at least one selector switch. Each selector switch of the selector system is in non-contact communication with either the backplane or with selector switches of another stage. Each of the selector switches in this staged crossbar switch operate in either of the two modes described above and have the same impedance matching characteristic.
Another aspect of the invention is a method of selecting one of a plurality of high throughput data lines comprising: inputting data pulses received on a selector switch which is coupled to the plurality of data lines; selecting, in a first mode of operation of the selector switch, one of the data lines and transmitting the data pulses received by the selector switch on the selected data line to a receiver; in a second mode of operation of the selector switch transmitting data pulses from the non-selected data lines to a positive supply; and matching the impedance of input lines into the selector switch in either said first or said second modes of operation.
Another aspect of the invention is a selector switch comprising: an input in communication with a data line; an output; and a selector circuit interconnecting the input to the output. The selector circuit is operable in a first mode to transmit data pulses received at the input from the data line to the output and operable in a second mode to discard data pulses received at the input from the data line. The selector circuit also matches the impedance of the data line in the first and the second modes of operation.